Blood Pressure Lab
What would you expect the measured systolic blood pressure to be with the arm raised above the head?
Lower than that measured with the arm in its normal position.
Finger Pulse Transducer Method
-Cuff is inflated until finger pulse disappears -Pressure released, blood flow returns=arterial systolic pressure
Invasive but accurate method of measuring BP?
-Inserting a catheter attached to a pressure gauge in an artery
Cuff Systolic Pressure?
-When the cuff pressure is raised above that of the artery, the artery collapses and pulse disappears; this is systolic
Hypertension treatment
ACE inhibitors and Angiotensin II antagonists
Tests for Hypertension
1. Measurement of cortisol, aldosterone and products of epinephrine (adrenaline) breakdown (e.g. catecholamines, metanephrines and vanillylmandelic acid [VMA]) in a 24 h urine sample; 2.Tests of renal function; and 3. Chest X-rays to exclude coarctation of the aorta which results in rib notching as a consequence of enlargement of intercostal arteries as part of the development of a collateral circulation.
What determines arterial blood pressure?
Cardiac output x peripheral resistance (heart rate x stroke volume x peripheral resistance) -anything that alters any of these can alter arterial blood pressure
How does blood flow?
From higher to lower pressure, so the contracting vessels generate a slightly higher pressure than the arteries -pressure falls progressively as it passes through the body
What determines cardiac output?
Heart rate x stroke volume
What would you expect if a sphygmomanometer cuff designed to be used on a small child's arm was used on an adult's arm?
Measured systolic and diastolic pressures would both be higher than the true pressures.
What is a finger pulse transducer, together with a sphygmomanometer, capable of determining?
Only systolic pressure. Systolic pressure is indicated by the first detection of a finger pulse, whereas diastolic pressure can only be determined using the auscultation method.
What do we usually refer to when speaking of blood pressure?
Systemic Arterial blood pressure, though all vessels have pressure
What is the basis for the sounds referred to as Korotkoff sounds?
Turbulent blood flow
Where is the best place to measure BP?
-At heart level (brachial artery)
How does gravity effect veins?
-Because the veins are distensible, the increased pressure tends to cause blood to pool in the veins, thereby decreasing the return of the blood to the heart (venous return) -counteracted by valves in the veins, which prevent blood backflow when standing or sitting -skeletal muscle contraction presses on the veins and helps to increase venous pressure
How is pressure generated?
-Contraction (systole) of the heart's ventricles
Role of each heartbeat
-Eject blood at sufficient pressure so that blood flow to the tissues is fast enough to provide the oxygen and nutrients that the cells require -waste products of metabolism must be removed constantly so that they do not accumulate in the tissues
How can the heart and blood vessels regulate BP?
-Elasticity and muscularity, alters cardiac output and peripheral resistance
You may have experienced difficulty in obtaining a blood pressure measurement when the arm was held above the head. Can you give a physiological explanation for this? Tip: Why do you think you experience fatigue when, for example, painting something above your head?
-It is very difficult to obtain a BP measurement when the arm is held above the head because the BP in the arm is much lower when the arm is raised; b/c of this, the arm is poorly perfused, which leads to fatigue when one is working with arms above the head
Highest BP/Lowest BP
-Left ventricle/right atrium
Normal BP Range?
-Many say 120/80 mmHg -100/60 to 140/90 -different in different arms sometimes, gentle exercise may lower it, strenuous exercise raises it
What can you conclude about the effect of cuff size on measured blood pressure? How can you explain this?
-Measurement of arterial BP requires the artery be uniformly compressed and the cuff pressure transferred to artery wall. -Too narrow, values too high -Too wide, values too low -Error from using a cuff too narrow is greater; most common mistake is using cuff too small for overweight person
Given the variation in pressure with height, blood pressure is normally referenced to heart level. Does this usually affect the pressure recorded from the upper arm?
-No because the position of the upper arm is normally at the level of the heart whether the person is standing, sitting or lying down
From your finger pulse recording, is there any way to determine diastolic pressure? Could a finger pulse measurement ever replace the stethoscope in determining diastolic pressure?
-No. The pulse recording does not have any obvious feature that allows diastolic pressure to be identified. Therefore, pulse recordings cannot replace the use of a stethoscope in determining diastolic pressure.
Units of BP
-Pressure can be measured as the height of liquid it can push up against gravity -blood and water have similar densities, so we can measure blood pressure in units such as cm of water, inches of water, or feet of water -Mercury is 13.5 times heavier than water (or blood) for the same volume -13th of the height of water filled (more practical) -mmHg
What does position effect?
-Regulation of BP and measurement of BP
What are some possible sources of error or variation in this technique of blood pressure measurement?
-Room noise may make it hard to hear the sounds -cuff may not be wrapped tight enough -cuff pressure released too fast, diastolic may not be accurately detected
How do your corrected standing leg blood pressures compare with your lying leg blood pressures? When do you think this method might be useful for blood pressure estimation?
-Should be similar when corrected for hydrostatic pressure contribution -may be self in certain research like taking standing BP from thigh or calf, then correcting -In exercise physiology study of the effects of arm wrestling on BP, where it should be necessary to obtain leg reading
Describe what you observed. How did the blood pressure in the leg compare with that in the same volunteer's arm? Explain your observations. From these findings, what is the correct posture when blood pressure is measured in any artery in the lower limb?
-Standing, BP is greater in the leg than the BP in the arm. Results from hydrostatic pressure on the column of blood. -Volunteer is lying down, arm and leg blood pressures should be very similar since both are at heart level -Therefore, lower limb BPs must always be measured with the subject lying flat or else corrected for the hydrostatic pressure contribution
What did you observe with the finger pulse amplitude when the arm is held above the head? What happened to the estimated systolic pressure? What do you think could account for this observation?
-The finger pulse amplitude decreases dramatically when the arm is held above the head. The systolic pressure will be harder to detect, but will be much lower than the BP measurement with the hand at heart level. The physiological reason that accounts for this observation is that the hand is more poorly perfused when held above the head; the systolic pressure is decreased by the hydrostatic pressure due to gravity.
How did deflating the cuff more quickly alter your blood pressure measurements?
-The heart rate limits the speed at which you can accurately record the blood pressure. The cuff needs to be deflated at a rate such that there is time for every heart beat to be detected as pressure falls. If a heart beat is missed, the pressure reading will be in error. -rate of deflation must be slow enough to capture every single pulse as a korotkoff sound; slower a person's heart rate, slower the cuff should be deflated
Diastolic Pressure
-The value when the arterial blood pressure is at its lowest - immediately before the contracting ventricle pushes blood into the arteries again
Clinically, two careful measurements of blood pressure with a one-minute interval are recommended, with a repeat measurement when there is any uncertainty.
-True
Direct Measurements of BP
-Used in intensive care -a plastic tube filled with saline connected to the vein -Central Venous Pressure -8-15 cmH2O or 6-11 mmHg. We can't do this for arteries because the apparatus would have to be about two meters tall!
Cuff Diastolic Pressure?
-When the normal diameter returns to the arteries and muffling sounds are heard, then nothing
Greatest increase in resistance?
-arterioles (also greater drop in BP) -arterioles, therefore, make the greatest contribution to the vascular peripheral resistance -resistance is increased by vasoconstriction and lowered by vasodilatation in order to regulate blood pressure.
When is arterial pressure at its lowest?
-as the ventricle relaxes (diastolic), immediate to the next contraction
Indirect Measurements of BP
-auscultatory method (stethoscope to listen to heart sounds and sphygmomanometer/blood pressure cuff) -Sphygmomanometer measures pressure in cuff -finger pulse transducer
Hypertension
-chronic condition characterized by a resting blood pressure of 140/90 mmHg or greater -repeated measurements at rest are often made -monitor blood pressure regularly over 24 hours, particularly because blood pressure during sleep should always be lower than blood pressure when awake (higher than 120/80 in sleep is indicative of hypertension)
Coarctation of the aorta
-congential -narrowing of the aorta in the region where the ductus arterioles inserts -increased resistance to blood flow -blood pressure is elevated above the site of the resistance. Conversely, blood pressure is lowered below this site -pulse wave also slowed -detected clinically by simultaneously feeling the radial and femoral arterial pulses. Normally these are synchronous but in coarctation of the aorta, the femoral pulse is delayed and felt after the radial pulse.
Acute blood loss will
-decrease arterial blood pressure -all in blood pressure is detected by the baroreceptors, which activate the cardiovascular control centers in the brain -stimulate the autonomic nerves to cause vasoconstriction (narrowing) of peripheral blood vessels and increase the heart rate and force of contraction -increases peripheral resistance, and the increased rate and force of cardiac contraction increase cardiac output, maintaining blood flow to the brain and other vital organs
Renin
-enzyme secreted by specialized kidney cells (granular cells of the juxtaglomerular apparatus). It breaks down angiotensinogen (produced in the liver and secreted into the blood) to angiotensin I, which is physiologically inactive
Why is femoral artery BP higher?
-higher below heart because of increased effects of hydrostatic pressure
When is arterial pressure at its highest?
-immediately after the ventricle contracts (systolic)
Epinephrine
-increased production raises blood pressure by causing arteriolar vasoconstriction and, hence, increased peripheral resistance -increases the heart rate and increases cardiac output.
Adrenal Cortex
-makes mineralocorticoids (aldosterone, which mainly affects salt excretion) and glucocorticoids (cortisol and corticosterone, which mainly affect glucose and protein metabolism) -cortical steroids or "corticoids" -increased production=increased salt absorption by kidneys=increased water absorption=expanded blood volume/BP/SV
Effect of Cuff Size
-measurement of arterial blood pressure using a sphygmomanometer requires that the artery be uniformly compressed and that the pressure in the cuff is accurately transferred to the artery wall -If the cuff is too narrow, values will be too high. -If the cuff is too wide, values will be too low.
Essential Hypertension
-no recognized causes (about 90% of adults with hypertension) -more likely to develop with age -lack of exercise, stress, alcohol intake and obesity, family history -the prime problem is an increased arteriolar resistance
Secondary Hypertension
-often possible to identify an underlying cause -increased adrenal corticoid production (Cushing's syndrome, primary aldosteronism); increased epinephrine (adrenaline) production by adrenal medullary tumors (pheochromocytoma); chronic renal disease; and coarctation of the aorta
Diastole
-period during the relaxation of the ventricles -During diastole, while the ventricles fill with blood returning from the veins in preparation for the next systole, blood continues to flow out of the arterial system into the capillaries. This flow is driven by the elastic recoil of the major arteries. Consequently, the arterial pressure decreases
How is arterial blood pressure measured in the body?
-pressure receptors (baroreceptors) in the aortic arch and the first part of the internal carotid artery - the carotid sinus -monitor the degree of stretch of the arterial wall -aortic arch baroreceptors are monitoring the pressure of blood flowing through the systemic arterial system whereas the carotid sinus receptors are specifically monitoring the pressure of the blood flowing to the brain
Acute expansion of blood volume will...
-raise arterial blood pressure -can happen with excess blood transfusion -cause peripheral vasodilatation and a decreased heart rate
Chronic Renal Disease
-result in fluid retention -stimulates increased renin production, resulting in increased angiotensin II levels, producing profound arteriolar vasoconstriction. Thus both stroke volume and peripheral resistance may be increased.
Korotkoff Sounds
-tapping sounds created by turbulent blood flow in arm -pressure is slowly being released from cuff, so systolic pressure is above that of the cuff, but diastolic is still below, so the artery opens in systole and collapses in diastole. -can be heard below diastolic in some cases
Systolic Pressure
-the peak pressure reached during the cardiac cycle -
Pulse Pressure
The difference between systolic and diastolic pressure in the arteries -gets smaller as vessel size decreases (so in the smallest vessels, there is only one blood pressure)
In the auscultation method for blood pressure measurement, what is diastolic pressure indicated by?
The disappearance of the sounds.
In the auscultation method for blood pressure measurement, what is systolic pressure indicated by?
The first detection of the sounds.
What is the basis for the sounds referred to as Korotkoff sounds?
Turbulent Blood flow
The terms systole and diastole usually refer to the _______ and _______, respectively, of the _______.
contraction; relaxation; ventricles